feat(ttp): rich ThreatActor STIX extensions via CustomExtension + CustomObject

- stix_custom.py: DecnetActorFingerprintExt (@CustomExtension) wrapping
  network_behavior (os_guess/hop_distance/tcp_fingerprint/timing_stats/
  phase_sequence/behavior_class/beacon fields/tool_guesses) and
  protocol_fingerprints (ja3_hashes/hassh_hashes/kex_order_raw/
  ssh_client_banners/tls_cert_sha256/payload_simhashes/c2_endpoints).
  XDecnetBehaveProfile (@CustomObject x-decnet-behave-profile) carrying
  full BEHAVE-SHELL observation envelopes + kd_digraph_simhash.
  FINGERPRINT_EXT_DEF singleton extension-definition SDO.
- Drop legacy flat x_decnet_ja3_hashes / x_decnet_hassh_hashes /
  x_decnet_c2_endpoints (pre-v1, no consumers).
- stix_export: _threat_actor() wired to behavior + observations;
  build_attacker_bundle/build_fleet_bundle grow observations parameter.
- Repo: list_observations_by_attacker + get_all_observations_for_export
  abstract + sqlmodel impl; all four export endpoints extended.
- 18 new tests; inter-DECNET round-trip (stix2.parse → typed objects)
  is the primary fidelity assertion.

decnet/web/db/sqlmodel_repo/observations.py

@@ -29,6 +29,21 @@ from decnet.web.db.models import Attacker, ObservationRow
 from decnet.web.db.sqlmodel_repo._helpers import _MixinBase
 
 
+def _to_envelope(row: "ObservationRow") -> dict:
+    """Map an ObservationRow to a BEHAVE envelope dict for STIX export."""
+    d: dict = {
+        "primitive": row.primitive,
+        "value": row.value,
+        "confidence": row.confidence,
+        "window": {"start_ts": row.window_start_ts, "end_ts": row.window_end_ts},
+        "source": row.source,
+        "evidence_ref": row.evidence_ref,
+    }
+    if row.identity_ref is not None:
+        d["identity_ref"] = row.identity_ref
+    return d
+
+
 class ObservationsMixin(_MixinBase):
     """Mixin: methods composed onto :class:`SQLModelRepository`."""
 
@@ -209,6 +224,36 @@ class ObservationsMixin(_MixinBase):
             )
             return (await session.execute(stmt)).scalar_one_or_none() is not None
 
+    async def list_observations_by_attacker(
+        self, attacker_uuid: str,
+    ) -> list[dict[str, Any]]:
+        """All observations for *attacker_uuid*, ordered by ``window_end_ts``
+        ASC, shaped as BEHAVE envelope dicts.
+        """
+        async with self._session() as session:
+            stmt = (
+                select(ObservationRow)
+                .where(ObservationRow.attacker_uuid == attacker_uuid)
+                .order_by(ObservationRow.window_end_ts)
+            )
+            rows = (await session.execute(stmt)).scalars().all()
+            return [_to_envelope(row) for row in rows]
+
+    async def get_all_observations_for_export(
+        self,
+    ) -> dict[str, list[dict[str, Any]]]:
+        """Return ``{attacker_uuid: [envelope, ...]}`` for all attackers."""
+        async with self._session() as session:
+            stmt = (
+                select(ObservationRow)
+                .order_by(ObservationRow.attacker_uuid, ObservationRow.window_end_ts)
+            )
+            rows = (await session.execute(stmt)).scalars().all()
+            result: dict[str, list[dict[str, Any]]] = {}
+            for row in rows:
+                result.setdefault(row.attacker_uuid, []).append(_to_envelope(row))
+            return result
+
     # Order desc(ts) reserved as the most-recent-first listing if a
     # paginated UI surface lands later. Not exposed today; named here
     # so a future grep finds the canonical desc-ts pattern.